Sea turtles remember their favourite restaurants

Sea turtles travel hundreds of miles back to their favourite feeding sites after breeding, retracing exactly same route they used up to five years earlier, a new tracking study has revealed.

Sea turtles are well-known to have a strong homing instinct for their nesting sites, but these new findings could have further implications for efforts to conserve sea turtles.

Annette Broderick at the University of Exeter in the UK, and colleagues used satellite transmitters to track 20 female loggerhead- and green turtles nesting at two sites in Cyprus. In doing so, they also recorded the longest ever breath-holding dive for any vertebrate, lasting an incredible 10 hours and 12 minutes.

"The extent to which turtles showed fidelity to specific foraging sites and routes was a surprise," says Broderick. "Marine turtles migrate hundreds of miles between breeding and foraging grounds, so it is amazing that they are able to return to exactly the same sites via very similar routes."

Repeat tracking

Broderick's group tracked the turtles' migration to foraging sites along the coast of Libya. Five years later, the team returned to the two beaches and recaptured five of the turtles. They then tracked these turtles' migration once more.

They were astonished to find that each of the five turtles returned to exactly the same foraging site as five years earlier, using exactly the same routes.

"The clever thing Broderick and her colleagues did was to manage to repeat-track the same turtles," says Graeme Hays, a sea turtle expert at the University of Swansea in the UK, who was not involved in the study. He adds that this is the first time researchers have managed the feat.

Map learning

Sea turtles have a homing instinct for their birthplace, which they return to for a few months every two to four years when they breed. "But turtles from the same nesting beach to not forage at the same locations," says Broderick.

"This suggests that at some stage they find a foraging site and are able to imprint on it and learn how to get back to it - true map-learning ability."

"We have known that sea turtles are very good navigators," says Hays, "so the fact that they can keep same course time after time is not totally surprising, but it is very neat to be able to demonstrate it."

Total protection

The conservation applications are important, says Broderick. "There is a lot of debate as to how to protect migratory species at sea, but for these turtles, it appears there is a real possibility of protecting them at all stages of their lives - at the nesting grounds, feeding grounds and potentially along the migratory corridors."

Protecting the turtles during their migration would require regional cooperation, since the turtles typically move through the territorial waters of three or four different countries. But Broderick points out that the migration only lasts a few months, making it easier to protect.

On 23 April, the International Maritime Organization agreed to divert shipping lanes off the southern coast of Spain in order to avoid important bottlenose dolphin foraging grounds.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.